One goal of tire manufactures is to improve tire design to increase the life of the tire. One measure of a tire's life is, of course, tire tread wear as a function of driven miles. When a tire is manufactured in accordance with a new design, it is essential that the manufacturer test the new tire to predict tire tread wear. To test tire tread wear for a new tire design, manufacturer's would typically mount a set of tires made in accordance with the new design on a vehicle and drive the vehicle on a test track. After driving a predetermined number miles, the new tires would be removed from the vehicle, tread wear would be measured, and the tires remounted to the vehicle for further testing by driving. Since the test and measurement made on one set of tires is not statistically sufficient to make a prediction of tire tread wear of all such tires, this process must be repeated on many sets of the tires made in accordance with the new design. Such an approach for determining tire tread wear is costly and time consuming.
It has been discovered that tire tread wear is functionally related to (i) evenness of the tire's force and (ii) tire tread slip at the tire's contact patch. If a tire has uneven force and/or excess tread slip at the contact patch, such tire could be expected to wear unevenly during its use. Non-destructive testing methods and apparatus have been developed that permit a manufacture to measure tire force and tire tread slip at the tire contact patch. From these measured values, wear of the tire is predicted.
Known non-destructive test apparatus includes tire contact pressure sensors that measure tire contact pressure in the contact patch and provide an electrical signal having a characteristic indicative of the measured tire contact pressure. The tire's contact pressure is indicative of the tire's force. Such known test apparatus includes a bearing plate over which a tire to be test is rolled. A contact pressure sensor is provided and includes a solid, longitudinally extending member having stain gages operatively secured thereto. The contact pressure sensor is received in an opening in the bearing plate and adapted to be engagable by the tire being tested as the tire rolls across the bearing plate. The strain gages are arranged to simultaneously measure vertical contact pressure, fore-aft shear stress, and lateral shear stress. It is also known to mount a plurality of such tire contact pressure sensors in a linear array across the bearing plate so as to be oriented perpendicular to the direction of travel of the tire being tested.
Other known non-destructive test apparatus includes slip sensors that measure tire tread slip in a contact patch and provide an electrical signal having a characteristic indicative of the measured tire tread slip. Such known test apparatus includes a bearing plate over which a tire to be test is rolled. A slip sensor is provided and includes a pointed pin. The pointed pin is received in an opening in the bearing plate and is arranged so as to protrude slightly above the bearing surface. As the tire rolls over the pin, the pin point sensor embeds itself in the tire tread. The pin bends commensurate with the tread slip. Strain gages are mounted to the pin and arranged so as to provide an electrical signal having a characteristic indicative of of the amount of tread slip.
Electronic circuitry or data acquisition equipment is used to collect data from tire contact pressure and/or tire tread slip sensors for later analysis and prediction of tire wear Such circuitry or data acquisition equipment is well known in the strain gage art.
The problem with known prior art non-destructive test apparatus is that the tire contact pressure sensors and the tire tread slip sensors are spaced a finite distance apart on the bearing block. Although both sensors measure tire contact pressure and tire tread slip in the same tire, the points of measurement on the tire under test are spaced apart. It has been found desirable to know both the tire contact pressure and the tire tread slip at common test points on the tire surface.